1. Field of the Invention
This invention relates to a process for producing modified polypropylenes containing propylene-ethylene copolymer blocks.
As a method for improving the impact resistance of polypropylenes while maintaining their desirable properties, a method for block-copolymerization wherein polymer blocks comprising an ethylene unit are introduced into the polypropylene has been known. The block copolymer can be produced by polymerizing propylene and ethylene stepwise in the presence of a stereoregular polymerization catalyst. The conventional method for this purpose comprises producing polypropylene and then copolymerizing ethylene or an ethylene-propylene mixture with the resulting polypropylene. If desired, polyethylene- or poly(ethylene/propylene)-block is additionally formed. By this conventional method, a modified polypropylene having some impact resistance is obtained. This impact resistance, however, cannot be said to be satisfactory high.